The present invention relates generally to an improved process for preparing metallic coatings, and more particularly to the preparation of ultra-thin metallic coatings utilizing liquid solutions containing metallic components, and wherein these solutions are exposed to plasma. According to the steps of the present invention, certain liquid solutions containing functional groups and metal precursors are initially applied to the surface of a substrate, with the coated substrate then being exposed to mild room temperature cold plasma, whereupon these groups and/or precursors are decomposed. The process occurs rapidly, and conversion to the metallic state likewise occurs rapidly, with the crystalline structure and alloy stoichiometry being subject to close control so as to deliver enhanced yields of a reaction product.
The present invention relates to novel techniques for depositing metals, metal blends and alloys, metal derivatives and complexes onto a variety of substrates including microporous substrates with the technique employing a plasma operation undertaken at substantially room temperature.
Soluble salts of precious metals for service as catalysts may be utilized in either aqueous or organic solvent based solutions to impregnate porous materials. Materials such as for example, zeolites, nanoporous materials, aerogels, activated alumina, microporous, ultrafiltration, nanofiltration and gas permeable membranes may be employed. Surface coat operations on porous or non-porous materials may be utilized for various applications, such as, for example, solar cells, fuel cell membranes such as Nafion, Webs used in barrier packaging films, carbon electrodes used in fuel cells and thin film displays. Aqueous or alcohol-based solutions are preferable for certain solvent sensitive substrate materials such as non-carbon-based aerogels and cellulose, whereas solvent-based solutions are preferable for hydrophobic materials such as Teflon@, PVDF, polypropylenes, and ceramics.
Monomer selection for the metallic component is important, with the preferred monomers being stable to vacuum conditions. Thus, unlike the conventional vapor techniques which rely heavily on the volatility of metal precursors, in the technique of the present invention, stability rather than volatility of the metal complex in vacuum is of primary importance. Also, the more preferred metal complex is a coordination compound of the metal. The use of active plasma for reducing adsorbed metal complexes to thin film of metals have been demonstrated by the present inventors in their U.S. Pat. No. 6,136,389 which substance of which is incorporated by reference herein.
When coated onto hollow fibers, or tubular membranes or flat films made from plastics, ceramics or carbon, films created pursuant to the present invention may serve in a variety of applications such as diesel filters, sterile filters, ion exchange media, biochemical-biowarfare agent filters, bio-organic reactors, and the like.
When coated onto nanoporous materials such as zeolites and other alumina-based materials, aerogels and carbon-based filters, and/or other carbon-based media, films created pursuant to the present invention may serve in a wide variety of catalytic applications in which the metallic coated porous particulate is added to wash coatings, fluidized beds, or alternatively, used to capture certain gases or chemicals from a flow, and thereafter followed by partial or total catalytic breakdown of the captured products.